The carbonylation of ethylene using carbon monoxide in the presence of an alcohol or water and a catalyst system comprising a Group VIII metal, e.g. palladium, and a phosphine ligand, e.g. an alkyl phosphine, cycloalkyl phosphine, aryl phosphine, pyridyl phosphine or bidentate phosphine, has been described in numerous European patents and patent applications, e.g. EP-A-0055875, EP-A-04489472, EP-A-0106379, EP-A-0235864, EP-A0274795, EP-A-0499329, EP-A-0386833, EP-A-0441447, EP-A-0489472, EP-A-0282142, EP-A-0227160, EP-A-0495547 and EP-A-0495548. In particular, EP-A0227160, EP-A-0495547 and EP-A-0495548 disclose that bidentate phosphine ligands provide catalyst systems which enable higher reaction rates to be achieved.
A problem with the previously disclosed catalyst systems is that although relatively high reaction rates can be achieved, the catalyst dies off quickly which necessitates the frequent replenishment of the catalyst and hence results in a process which is industrially unattractive.
WO 96/19434 disdoses a particular group of bidentate phosphine compounds which can provide remarkably stable catalysts which require little or no replenishment and the use of such bidentate catalysts in a process for the carbonylation of ethylene with carbon monoxide.